AS LEVEL- Biology- Biological molecules (1)

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  • Biological molecules (1)
    • Water
      • Hydrogen bonding occurs as water is a polar molecule so it has a partial negative charge at one region of the molecule (oxygen) + a partial positive charge elsewhere (hydrogen)
      • Properties
        • Solvent
          • 1) Lots of important substances in biological reactions are ionic. This means they're made from 1 positively  charged atom or 1  negatively chrged atom
          • 2) Because water is polar, the slightly positive end of a water  molecule will be attracted to the negative ion, + the slightly negative end of a water  molecule will be attracted to the positive ion
          • 3) This means the ions will get surrounded by the water  molecule
          • 4) Water's polarity makes it a good solvent in living  organisms eg. in humans important ions can dissolve in the water in blood + then be transported around the body
        • High specific heat capacity
          • Energy needed to raise the temp of 1 gram of substance by 1 degree celsius
          • The  hydrogen bonds  between water molecules can absorb lots of energy. So water has a high specific heat  capacity- it takes lots of energy to heat it up
          • This means water doesn't experience rapid temp change which is one of the properties that makes it a good habitat- the temp under water is likely to be more stable than is on land
        • Cohesive  forces
          • The attraction between molecules of the  same type. Water molecules are very  cohesive as they're polar
          • This helps water flow, making it good for transporting substances. It also helps water up plant stems in the transpiration stream
        • High latent heat of evapouration
          • It takes lots of heat energy to break the hydrogen bonds between water molecules
          • So water has a high latent heat of evapouration- Lots of energy is used up when water evapourates
          • This is useful for living  organisms  because it means water is good for  cooling things. When sweat evapourates it cools the surface of the skin
        • Low desity when solid
          • At low temps water freezes- turns from a liquid into a solid
          • Water molecules are held further apart in ice as each water  molecule holds 4  hydrogen bonds to other water  molecules  making it a lattice shape. This makes ice less dense  than liquid water- which is why ice floats
          • This is useful for living  organisms as, in cold temps ice forms an insulating  layer on top of water- the water  below doesn't freeze. So organisms that live in water don't freeze and can still move around
    • Carbohydrates (C, H, O)
      • The monomers that make up carbohydrates are called  monosaccharides
      • Most carbohydrates are polymers. A polymer is a molecule made up of many similar, smaller molecules bonded together
      • Glucose
        • Structure; Glucose is a monosaccharide with 6 carbon atoms- called a hexose monosaccharide
        • 2 forms; alpha + beta
          • Difference; The hydroxyl group on carbon 1 is below the ring in alpha glucose + above the ring in beta glucose
        • Structure to function; Glucose is small so it's easier to transport by facilitated diffusion. Glucose is polar so it can make hydrogen bonds + can dissolve. Glucose can easily be broken down to release enegry
      • Condensation Reactions
        • Occurs when a chemical bond is built up between 2 monomers+ water  is released
        • A 1-4 glycosidic bond occurs  between 2 alpha glucose molecules, when the hydroxyl on carbon 1 of the glucose molecule interacts with the hydroxyl group on carbon 4 of the other glucose molecule forming the 1-4 glycosidic bond + water is released
        • Glucose + Fructose = sucrose
        • Glucose + galactose = lactose
      • Pentose Monosaccharides
        • A pentose monosaccharide contains 5 carbon atoms + has a 5 membered ring eg. ribose + deoxyribose
        • Difference between hexose + pentose; Hexose means there are 6 carbon atoms and pentose means there are 5 carbon atoms
        • Starch- Found in plants as a chemical energy store
          • Structure; Starch is a mixture of 2 polysaccharides made by joining alpha glucosemolecules by glycosidic bonds
          • Made of 2 different polysaccharides
            • Amylose- Structure; long unbranched chain of alpha glucose, 1-4 glycosidic bonds, coiled because of the angle of the glycosidic bond
            • Amylopectin- Structure; long branched chain of alpha  glucose, 1-4 + 1-6 glycosidic bonds
          • Structure to function; Starch is compact so it doesn't take up lots of room + you can fit more in a small space. Starch is insoluble so it doesn't  affect the water potential of cells which  means it has no impact on osmosis. Starch is branched so there's more ends of the molecule for enzymes to attach in order to add or remove glucose molecules
        • Glycogen- Energy storage molecule in animals
          • Structure; Glycogen is made of alpha glucose  molecules joined by 1-4 + 1-6 glycosidic bonds. Its structure is  very similar to amylopectin but has more branches
          • Structure to function; Glycogen is compact so it doesn't take up lots of room + you can fit more in a small space. Glycogen is insoluble so it doesn't  affect the water potential of cells which  means it has no impact on osmosis. Glycogen is branched so there's more ends of the molecule for enzymes to attach in order to add or remove glucose molecules
        • Cellulose- Major component of cell walls in plants
          • Structure; Cellulose is made of beta glucose molecules joined by 1-4 glycosidic bonds. However every second beta glucose molecule has to be flipped so that the hydroxyl groups are in close contact to form the glycosidic bonds. This means the chain produced is straight. Cellulose molecules join to each other by hydrogen bonds forming  microfibrils
          • Structure to function; Cellulose is strong due to the hydrogen bonds, this allows it to provide tensile strength to support plant cells. Cellulose is insoluble so it doesn't  affect the water potential of cells which  means it has no impact on osmosis

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